Significant Contribution of Multidecadal Ocean Variability in Recent Warming of Northern Continents

Surface air temperature (SAT) over Northern Hemisphere (NH) continents has risen sharply in recent decades. Are the substantially larger recent trends indicative of accelerated secular warming, multidecadal natural variability, or both? An observations-based estimate for the secular warming of continents is obtained, factoring for multidecadal natural variability which is characterized from two SST datasets to bracket the diagnosis. SAT reconstruction shows one-third of the recent (1970-2009) winter SAT trend, averaged over NH continents, linked with SST natural variability which dominates trends over central-eastern North America, Greenland, and northern Eurasia. Atlantic Multidecadal Variability (AMV) is a significant contributor, in part, from anomalous thermal advection. Its contribution to North American—Greenland SAT trends is impressive (one-third), indicating prospects of some reprieve in the AMV flip-phase. Factoring for multidecadal natural variability yields reduced estimates for the post-1970 secular warming, but these remain larger than their full-century counterparts by a factor of 2-3.